Field of the Invention
The present invention relates to a nuclear power plant cable and a monitoring system therefor, and more particularly, to a nuclear power plant cable whose damage or life span being monitored in real time and a nuclear power plant cable monitoring system that is capable of monitoring the state of a nuclear power plant cable in real time, without having any physical destruction or chemical changes.
Background of the Related Art
Recently, with the drastic development of nuclear power generation technology like fourth generation nuclear power plants, focusing on the design technology of the nuclear power plant, the extension of the life span of operating equipment, and the cables needed for the operation of the equipment is appearing. After the Fukushima nuclear power plant accident, especially, high focusing on the stability of the equipment installed in the nuclear power plant appears, and accordingly, focusing on the stability of all kinds of cables installed in the nuclear power plant also appears. The nuclear power plant cables used in the nuclear power plant should provide radiation resistance, heat resistance, chemical resistance, and reliability for the use of a long period of time.
The fourth generation nuclear power plant is provided to strength the stability and economic effects of the nuclear power plant, which means the nuclear power plant available for about 60 or more. Like this, in case where the nuclear power plant is used for a long period of time, the cables for transmitting power and electrical signals to a variety of equipment of the nuclear power plant become ones of the most important equipment. Unlike other equipment of the nuclear power plant, the cables are installed basically as an infrastructure, and after the installation, it is impossible for them to be separated, disassembled and moved, without having the stop of the activation of the nuclear power plant. So as to ensure the stability of the cables installed in the nuclear power plant, without any stop, accordingly, the states of the cables should be monitored continuously, and further, the life spans of the cables should be also measured.
There are various methods for monitoring the nuclear power plant cables installed in the nuclear power plant. For example, the first method makes use of chemical properties of the cables. That is, the correlation relation between the variation of the chemical properties of the insulating materials of the cables and the thermal aging of the cables is checked. In more detail, the first method makes use of infrared spectrophotometer, oxidation induction time, thermo gravimetric analysis TGA and the like. The second method makes use of mechanical properties of the cables. That is, the variations of the compression rate, density, and elasticity rate of the cables are measured. In the second method, especially, an EAB (Elongation At Break) using the elongation rate is typically used for estimating the life spans of the cables. However, the first and second methods making use of the chemical and mechanical properties of the cables are limited in application in accordance with the materials of the cables, and further, they cause the destruction of the cables.
On the other hand, there is an electrical method for applying power to the insulating materials of the cables to sense their variation degrees through the thermal aging. That is, this method makes use of insulation resistance, voltage resistance, dielectric loss, dielectric tangent, partial discharge and the like. By the way, the electrical method is applicable to all kinds of materials, but it is hard to quantitatively display the correlation relation with the thermal aging.
So as to expect the life spans of the nuclear power plant cables in the conventional practices, accordingly, the existing cables should be removed and disassembled to check whether the insulation layers of the cables are damaged or not. However, it is hard to conduct the removal of the cables over the whole region of the nuclear power plant. Thus, the test of the cables is carried out only on a given region of the nuclear power plant, but according to the characteristics of the nuclear reactor having radiation emitted therefrom, the cables do not have the same aging degrees over the whole region of the nuclear power plant. So as to apply the removal of the cables and the measurement of the life spans of the cables, further, the activation of the nuclear power plant should stop or restart, which requires astronomical costs, and demander load caused by the stop of the activation of the nuclear power plant is added undesirably to the load of the operation of the nuclear power plant. The aged cables or damaged cables in the existing cables installed in the nuclear power plant should be exchanged with new ones, but it is very hard to remove the cables because of the structures of the ducts of the cables of the nuclear power plant. Furthermore, the removal of the cables needs very high costs.